Configuring Veritas Volume Manager 515

Guidelines for configuring storage

Dirty region logging guidelines

Dirty region logging (DRL) can speed up recovery of mirrored volumes following a system crash. When DRL is enabled, Veritas Volume Manager keeps track of the regions within a volume that have changed as a result of writes to a plex.

Note: Using Dirty Region Logging can impact system performance in a write- intensive environment.

For more information, see “Dirty region logging” on page 60.

Striping guidelines

Refer to the following guidelines when using striping.

■Do not place more than one column of a striped plex on the same physical disk.

■Calculate stripe-unit sizes carefully. In general, a moderate stripe-unit size (for example, 64 kilobytes, which is also the default used by vxassist) is recommended.

■If it is not feasible to set the stripe-unit size to the track size, and you do not know the application I/O pattern, use the default stripe-unit size.

Note: Many modern disk drives have variable geometry. This means that the track size differs between cylinders, so that outer disk tracks have more sectors than inner tracks. It is therefore not always appropriate to use the track size as the stripe-unit size. For these drives, use a moderate stripe-unit size (such as 64 kilobytes), unless you know the I/O pattern of the application.

■Volumes with small stripe-unit sizes can exhibit poor sequential I/O latency if the disks do not have synchronized spindles. Generally, striping over disks without synchronized spindles yields better performance when used with larger stripe-unit sizes and multi-threaded, or largely asynchronous, random I/O streams.

■Typically, the greater the number of physical disks in the stripe, the greater the improvement in I/O performance; however, this reduces the effective mean time between failures of the volume. If this is an issue, combine striping with mirroring to combine high-performance with improved reliability.

■If only one plex of a mirrored volume is striped, set the policy of the volume to prefer for the striped plex. (The default read policy, select, does this automatically.)